What you need to know about Anti venom.

The following interesting article on antivenom was provided by Johan Marais, of the African Snakebite Institute.

The only effective treatment for severe snakebite envenomation from a potentially deadly snake is antivenom. Using antivenom is not easy and it has its disadvantages, but in the right hands, and at the right time, it is life-saving. However, people have a poor understanding of how it works, and there are endless myths about antivenom killing more people than the snake venom itself. Not to mention numerous miracle cures for snakebite including antihistamine, cortisone and Vitamin C.

Antivenom for snakebite was first used in South Africa in 1886, and local production started in Pietermaritzburg in 1901. Production was for small quantities, with most of the antivenom still being imported from the Pasteur Institute in Paris, France. In those days one could purchase a 10ml of cobra or mamba antivenom from Mr. F.W. FitzSimons, Director of Port Elizabeth Museum.

In 1928 the South African Institute for Medical Research (SAIMR) started producing antivenom which was initially limited to Cape Cobra and Puff Adder venom, but Gaboon Adder venom was eventually included in the manufacturing process in 1938. Around this time the first monovalent Boomslang antivenom was also developed. Rinkhals venom was then added, followed by the production of different mamba antivenoms in the ’50s and ’60s, and in 1971 the venom of the Forest Cobra, Mozambique Spitting Cobra and Snouted Cobra were included to produce a polyvalent antivenom that is still manufactured today.

Antivenom is produced using a variety of animals including sheep, donkeys and camels; in South Africa we use horses. A horse is either hyperimmunized with a single snake venom (Boomslang antivenom) or against venoms from a variety of snake species (polyvalent antivenom). This is done over an extended period of time by injecting small quantities of venom into an animal. The quantity is increased over time and the animal gradually builds up an immunity. Once the animal is immunized, plasma is collected. The plasma then goes through a process to remove proteins, pyrogens, and microbes. The polyvalent antivenom is available in 10ml glass vials, costs near R1,350.00 a vial, and can last three years if stored in a refrigerator. Antivenom is now produced by South African Venom Producers in Sandringham, Johannesburg, and the polyvalent antivenom covers the Puff Adder, Gaboon Adder, Rinkhals, Green Mamba, Jameson’s Mamba, Black Mamba, Cape Cobra, Forest Cobra, Snouted Cobra, and Mozambique Spitting Cobra.

Few snakebite victims are actually treated with antivenom (less than 15% of those hospitalised after a snakebite) as it is scarce, expensive and can have disastrous side-effects. The biggest dangers are an acute allergic reaction (anaphylaxis) or serum sickness that can affect the immune system several days after treatment.

Snakebite victims are not automatically injected with antivenom as most of them never experience symptoms severe enough to justify its use. The majority of snakes have full control over their venom glands and are quite reluctant to waste their venom on humans. Snakes very often give ‘dry’ bites (no envenomation), with victims showing no symptoms from the bite. However, snakes can sometimes inject a small amount of venom that will cause mild discomfort and few symptoms, but no serious risks are present in this case. Such patients are usually hospitalised for a day, carefully monitored and then sent home.

Antivenom should only be used in a hospital environment and only when absolutely necessary. Patients will already be on a drip, and the antivenom will be administered intravenously. Intraosseous administration may be a consideration if veins prove difficult to find. Most doctors will start with an initial dosage of 6-10 vials. In a recent mamba bite, which was quite severe, the victim received 40 vials before starting to recover. This was an exceptional case and most victims receive only 10-12 vials of polyvalent antivenom or 2 vials of monovalent Boomslang antivenom. As mentioned, some snakebite victims display an allergic reaction to antivenom, which happens in more than 40% of all cases. Some victims go into anaphylactic shock, which is a life-threatening medical condition, and must urgently be treated with adrenaline. The allergic reaction has to do with the fact that our antivenom is made from horse blood, and the people who display symptoms are reacting to impurities in the antivenom.

Additional processes in the manufacturing of the polyvalent antivenom could reduce the incidences of anaphylaxis. Antivenom should only be used if there is a threat to life and limb, by a qualified medical doctor, and in a hospital environment. Antivenom is highly effective and the sooner it is administered, the better for the snakebite victim. In neurotoxic bites (mambas and most cobras) the venom may soon affect breathing. These snake bites are the cause of the majority of fatalities, whereas cytotoxic bites (Puff Adder and Spitting Cobra) often result in swelling, blistering, and necrosis.

The sooner antivenom is administered, the better the chances are of preventing necrosis and reducing the extent thereof. It is a popular myth that more people die from the antivenom than from the snake venom itself, but anaphylaxis is common and manageable if dealt with urgently and in the right manner

Source:  Johan Marais, African Snakebite Institute.

http://www.africansnakebiteinstitute.com

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